The present invention relates to a system for dissipating heat from a high power density device (HPDD). More specifically, the invention relates to a system that helps in effective dissipation of heat at a distance away from the HPDD.
Electronic devices such as central processing units, graphic-processing units, laser diodes etc. generate a lot of heat during operation. In case the generated heat is not dissipated properly from high power density devices, this may lead to temperature buildup in these devices. The buildup of temperature can adversely affect the performance of these devices. For example, excessive temperature buildup may lead to malfunctioning or breakdown of the devices. So, it is important to remove the generated heat in order to maintain normal operating temperatures of these devices.
The heat generated by HPDD is removed by transferring the heat to ambient atmosphere. Several methods are available to transfer heat from a HPDD to the atmosphere. For example, an electric fan placed near a HPDD can blow hot air away from the device. However, a typical electric fan requires a large amount of space and thus it may not be desirable to place a fan near the HPDD due to space constraints in the vicinity of the HPDD. In case of notebook computers or laptops, there is additional constraint on the positioning of the fans due to the compact size of these devices. For at least the foregoing reasons, it would be desirable to provide heat dissipation (e.g. using a fan) at a location away from the HPDD.
Another way to dissipate heat from a HPDD involves the use of a large surface area heat sink. Essentially, the heat sink is placed in contact with the HPDD to transfer heat away from the HPDD into the heat sink. The transferred heat is then dissipated through the surface area of the heat sink, thereby reducing the amount of temperature. buildup in the HPDD. In case a significant amount of heat is generated, a larger-sized heat sink is necessary to adequately dissipate the heat. Also in some cases the heat sink cannot be placed adjacent to HPDD due to form factor restriction. This may be due to non-availability of space near the HPDD or due to other devices/components located nearby that cannot withstand the rise in temperature due to dissipated heat. One way of dealing with the form factor limitation is to place a heat sink at a sufficiently large distance from the HPDD. In this case, heat has to be transferred from HPDD to the heat sink before being dissipated to the atmosphere.
A heat pipe is a device that can effectively transfer heat from one point to another. It consists of a sealed metal tubular container whose inner surfaces have a capillary wicking material. A fluid flows along the wick structure of the heat pipe. FIG. 1 shows a heat pipe 101. It has an inner lining 103 of micron scale wick structures. A HPDD 105 transfers heat to an end 107 of heat pipe 101. Liquid at end 107 absorbs the heat, evaporates and moves to a cold end 109 of the heat pipe. The evaporated vapor comes in contact of cold end 109, condenses and dissipates heat. The condensed liquid moves back to end 107 by gravitation or by capillary action of the inner lining 103. The wick like structure of lining 103 provides capillary driving force to return the condensate to end 107.
A Heat pipe is useful in transferring heat away from the HPDD when the form factor and other constraints limit dissipation of heat near the HPDD itself. Further, it has the ability to transport heat against gravity with the help of porous capillaries that form the wick.
Heat pipes exploit liquid-vapor phase change properties. Thus, maximum heat transfer is limited by vapor/liquid nucleation properties. Interface resistance between the metal surface and the liquid layer also limits the maximum heat flow. Heat pipes do not solve the problems of interface resistances at the hot source end and the cold sink end. Interface resistance between the metal surface and the liquid layer also limits the maximum heat flow. It is also not possible to cool multiple hot sources using a single heat pipe. Often these heat pipes contain CFC fluids that are not environment-friendly. The performance of these heat pipes depend on the orientation of the heat pipe structure with respect to the gravitational forces, operating temperatures, and the nature of fluids in the loop. The dependence of performance on orientation restricts the flexible positioning of heat pipes.
The above-discussed limitations of heat pipes have made forced fluid cooling an attractive option. The forced fluid cooling is based on circulating water through a HPDD. Water carries away heat from the HPDD and dissipates the heat at a sink placed at a distance. The heat is dissipated at the sink using fluid-fluid heat exchangers such as finned radiators with natural or forced convection. In forced fluid cooling, more than one HPDD can be cooled in a single loop.
However, the use of water in forced fluid cooling has some limitations. The low thermal conductivity of water limits its effectiveness as a heat transfer fluid. So, in this case only mode of transfer of heat is convection. Transfer of heat by conduction is negligible. Also, water is circulated using mechanically moving pumps that are largely unreliable, occupy large volumes, and contribute to vibration or noise.
U. S. Pat. No. 3,654,528 titled xe2x80x9cCooling Scheme For A High Current Semiconductor Device Employing Electromagnetically-Pumped Liquid Metal For Heat And Current Transferxe2x80x9d describes the use of liquid metal to spread heat uniformly in the heat sink placed in contact with a wafer. However, this patent describes heat dissipation in the proximity of the heat-generating device and does not address to the form factor limitation. Further, the use of electromagnetic (EM) pumps requires an extra power supply that generates heat. Removal of this additional heat adds to the burden.
In light of the above discussion it is clear that methods provided by the prior art do not satisfactorily address the issue of removal of heat at a desirable distance away from a high power density device. Thus there is a need for a flexible method for managing dissipation of heat at a distance away from the high power density device.
It is an object of the invention to provide an efficient and flexible method of dissipating heat away from a high power density device.
It is another object of the invention to provide a system for effective dissipation of heat from high power density devices, while taking care of the form factor limitations.
It is another object of the invention-to provide a system for the effective transfer of heat from high power density devices at a predefined distance away from the device.
It is another object of the invention to provide a system that uses electromagnetic pumps for circulating liquid metal for carrying away the heat generated by high power density device.
It is another object of the invention to provide electromagnetic pumps that use polymers or refractory metals as the material of construction of the conduit and gallium indium alloy as the liquid metal.
It is yet another object of the invention to provide an electromagnetic generator to power the electromagnetic pumps.
It is yet another object of the invention to enable the use of fluid-fluid heat exchangers (including condensers, radiators etc.) for dissipating heat generated by high power density device.
The invention provides a system for effective removal of heat from a high power density device and dissipating the heat at a distance. The system in accordance with the invention has a solid-fluid heat exchanger mounted on a high power density device. A closed conduit carrying liquid metal passes through the solid-fluid heat exchanger. The liquid metal is circulated in the conduit. The liquid metal carries away the heat generated by the high power density device and dissipates it at a heat exchanger or heat sink provided at a predefined distance away from the device. This system is highly flexible and can be used in different embodiments depending on form factor limitations. The same conduit (carrying the liquid metal) can be used for carrying heat away from multiple devices. Multiple pumps arranged in series or parallel arrangements may also be provided. Two or more loops (of the conduit) can use a common pump or common solid-fluid heat exchanger. A loop can dissipate heat, which is further carried away by another loop. More and more complex network of loops as desired can be formed.